Serial i/o using jtag tck and tms signals

ABSTRACT

The present disclosure describes a novel method and apparatus of using the JTAG TAP&#39;s TMS and TCK terminals as a general purpose serial Input/Output (I/O) bus. According to the present disclosure, the TAP&#39;s TMS terminal is used as a clock signal and the TCK terminal is used as a bidirectional data signal to allow serial communication to occur between; (1) an IC and an external controller, (2) between a first and second IC, or (3) between a first and second core circuit within an IC.

CROSS REFERENCE TO RELATED PATENTS

This application is a divisional of prior application Ser. No.12/712,572, filed Feb. 25, 2010, currently pending;

Which was a divisional of prior application Ser. No. 12/140,404, filedJun. 17, 2008, now U.S. Pat. No. 7,698,614, granted Apr. 13, 2010;which was a divisional of prior application Ser. No. 11/051,707, filedFeb. 4, 2005, now U.S. Pat. No. 7,404,128, granted Jul. 22, 2008;Which claims priority from Provisional Application No. 60/545,704, filedFeb. 17, 2004.

This application is related to U.S. application Ser. No. 11/015,816,filed Dec. 17, 2004, titled “JTAG Bus Communication Method andApparatus”, U.S. application Ser. No. 10/983,256, filed Nov. 4, 2004,titled “Removable and Replaceable TAP Domain Selection Circuitry”, nowU.S. Pat. No. 7,200,783, issued Apr.3, 2007, and U.S. Pat. No.6,393,081, titled “Plural Circuit Selection Using Role Reversing ControlInputs” all of which are incorporated herein by reference.

FIELD OF THE DISCLOSURE

This disclosure relates in general to circuit design and in particularto improvements in the design of IEEE 1149.1, approved Feb. 15, 1990,TAP interfaces of devices (such as ICs, cores, and/or other circuits)for enhancing communication to and from the devices during operationssuch as, but not limited too, (1) test operations, (2) debug operations,(3) trace operations, (4) emulation operations, (5)in-system-programming operations, and (6) other, as needed, operations.

BACKGROUND OF THE DISCLOSURE

Today the IEEE 1149.1 (JTAG) Test Access Port (TAP) interface is usedfor many different applications. While initially designed to provide aserial test interface on ICs to facilitate board testing, the TAPinterface now serves as a serial interface for additional IEEE standardsfor such things as emulation, trace, and debug (IEEE 5001) of ICs andcores, mixed signal testing (IEEE 1149.4) of ICs and cores, advanced ICto IC interconnect testing (IEEE 1149.6), embedded core testing (IEEE1500), and in-system-programming of circuits in ICs and cores (IEEE1532).

An IC may contain many embedded 1149.1 based TAP architectures (TAPdomains). Some of these TAP domains are associated with intellectualproperty (IP) core circuits within the IC, and serve as accessinterfaces to test, debug, trace, emulation, and in-system-programmingcircuitry within the IP cores. Other TAP domains may exist in the ICwhich are not associated with cores but rather to circuitry in the ICexternal of the cores. Further, the IC itself will typically contain aTAP domain for operating IC level test, debug, trace, emulation, andin-system-programming, as well as the boundary scan register associatedwith the IC's input and output terminals.

From the above, it is clear that TAP domains are being used in evergrowing numbers in devices, such as ICs and cores, for test, debug,trace, emulation, in-system-programming, and other types of operations.

The present disclosure describes novel methods and apparatuses for usinga TAP Domain's test mode select (TMS) and test clock (TCK) interfaceterminals as a general purpose serial Input/Output (I/O) bus. Accordingto one aspect, the TMS terminal is used as a clock signal and the TCKterminal is used as a bidirectional data signal to allow serialcommunication to occur between; (1) an IC and an external controller,(2) between a first and second IC, and (3) between a first and secondcore circuit within an IC. The use of TMS as a clock signal and TCK as adata signal does not effect the standardized operation of 1149.1 TAPDomains, since the TMS clock and TCK data operations occur when the TAPDomains are in a steady state.

FIG. 1 illustrates a simple example of an IEEE 1149.1 TAP domain 102.The TAP domain includes a TAP controller 104, an instruction register(IR) 106, at least two data registers (DR) 108, and multiplexercircuitry 110. The TAP domain interface consists of a TDI input, a TCKinput from an input buffer 116, a TMS input from an input buffer 118, aTRST input from an input buffer 120, and a TDO output.

An input buffer will exist on the TDI input if the TAP Domain is used byitself in an IC or if it is the first TAP Domain in a series of seriallyconnected TAP Domains in an IC. Also an output buffer will exist on theTDO output if the TAP Domain is used by itself in an IC or if it is thelast TAP Domain in a series of serially connected TAP Domains in an IC.

In response to TCK and TMS control inputs to TAP controller 104, the TAPcontroller outputs control to capture data into and shift data througheither the IR 106 from TDI to TDO or a selected DR 108 from TDI to TDO.The data shifted into IR 106 is updated and output on bus 114 to othercircuits, and the data shifted into a DR 108 is updated and output onbus 112 to other circuits. DR 108 may also capture data from othercircuits on bus 112 and IR 106 may capture data from other circuits onbus 114. In response to a TRST input to the TAP controller 104, the TAPcontroller, IR and DR are reset to known states. The structure andoperation of IEEE 1149.1 TAP domain architectures like that of FIG. 1are well known.

FIG. 2 illustrates the state diagram of the TAP controller 104. All IEEE1149.1 standard TAP controllers operate according to this state diagram.State transitions occur in response to TMS input and are clocked by theTCK input. The IEEE 1149.1 TAP state diagram is well known.

FIG. 3 illustrates an example scan path system 302 where a number of TAPdomain 102 interfaces of ICs 306-312 or embedded cores 306-312 withinICs are connected together serially, via their TDI and TDO terminals, toform a scan path 302 from TDI 304 to TDO 307. Each TAP domain 102 of theICs/cores 306-312 are also commonly connected to TCK 314, TMS 316, andTRST 318 inputs. The scan path's TDI 304, TDO 307, TCK 314, TMS 316, andTRST 318 signals are coupled to a controller 320, which can serve as atest, debug, trace, emulation, in-system-programming, and/or otherapplication controller. While only four TAP domains 102 of ICs/cores306-312 are shown, any number of IC/core TAP domains may exist in scanpath 302, as indicated by dotted line 322. The scan path 302 arrangementof IC/core TAP domains is well known in the industry.

As seen in FIG. 3, if data is to be input to TAP domain 102 of IC/core312 from controller 320 it must serially pass through all leading TAPdomains of ICs/cores 306-310. Further, if data is to be output from TAPdomain 102 of IC/core 306 to controller 320 it must pass through alltrailing TAP domains of ICs/cores 308-312. Thus a data input and/oroutput latency exists between a target TAP domain in scan path 302 andcontroller 320, due to having to serially traverse intermediate TAPDomains. To further exacerbate the problem, the shifting frequency ofthe scan path 302 is limited by the slowest shifting TAP domain in thescan path.

For example, if a target TAP domain (i.e. the one where data is to beinput to or output from) can shift at 100 MHz, but one or more of theother TAP Domains that need to be serially traversed during the input oroutput operation can only shift at 10 MHz, the data transfer between thecontroller 320 and the target TAP domain will be limited to thefrequency of the slower TAP domain, i.e. 10 MHz. Due to the abovementioned data latency and shift frequency limitation problems, it isclear that the data communication bandwidth between a target TAP domainand controller 320 is not optimized.

As will be seen later, the present disclosure provides a way toeliminate the above mentioned data latency and shift frequencylimitation problems by making use of the direct TMS 316 and TCK 314connections between the TAP domains of ICs/cores 306-312 and controller320. Having a direct connection for data input and output between thecontroller 320 and the TAP domains 102, via the TMS and TCK connections,provides improved data communication bandwidth during test, debug,trace, emulation, in-circuit-programming, and other types of operations.Further, using the direct TCK and TMS connections as a serial bus fordata input and output between controller 320 and TAP domains 102 onlyinvolves the controller and the targeted TAP domain. Non-targeted TAPdomains are not aware of or effected by the direct TMS and TCKcommunication.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure provides a method and apparatus of communicatingdata between; (1) an IC in a scan path and a controller of the scan pathusing the TMS and TCK connections that exists between the IC andcontroller, (2) a first IC of a scan path and a second IC of the scanpath using the TMS and TCK connections that exist between the ICs, (3) afirst core circuit of a scan path in an IC and second core circuit ofthe scan path of the IC using the TMS and TCK connections that existbetween the cores.

The TMS and TCK data I/O communication occurs while the TAP controllerof the TAP domains of the IC/core are in a steady state. Thus the TMSand TCK I/O communication does not disturb or modify the state of TAPdomains of the IC/core in a scan path. The TMS and TCK I/O communicationis achieved by adding circuitry to the IC/core and coupling thecircuitry to the TMS and TCK terminals of the IC's/core's TAP domain.

When enabled by control output from the IC's/core's TAP domain, theadded circuitry becomes operable to input data from the TAP domain's TCKterminal in response to a clock signal received at the TMS terminal, orto output data onto the TAP domain's TCK terminal in response to a clocksignal received at the TMS terminal. Conventional controllers 320coupled to the TAP domain's TMS and TCK terminals are improved,according to the present disclosure, such that they are operable to; (1)output clocks on the TMS signal to TAP domains, (2) input data on theTMS signal from TAP domains, and (3) output data on the TMS signal toTAP domains.

BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS

FIG. 1 illustrates a conventional IEEE 1149.1 TAP domain architecture.

FIG. 2 illustrates the state diagram of a conventional IEEE 1149.1 TAPcontroller.

FIG. 3 illustrates a conventional arrangement of ICs or cores within ICswith their TAP domains connected in a scan path and the scan pathcoupled to a controller.

FIG. 4 illustrates the scan path and controller arrangement of FIG. 3adapted for serial I/O communication according to the presentdisclosure.

FIG. 5 illustrates serial I/O communication circuitry coupled to a TAPdomain according to the present disclosure.

FIG. 6A illustrates the entry into and exit from the TAP controller'sRun Test/Idle state.

FIG. 6B illustrates the serial I/O operation of the present disclosureoccurring while the TAP controller is in the Run Test/Idle state.

FIG. 6C illustrates the timing of the TCK and TMS signal transitionsduring serial I/O operations of the present disclosure.

FIG. 7 illustrates the Serial I/O Circuit of the present disclosure.

FIG. 8 illustrates the I/O Controller circuit of the present disclosure.

FIG. 9 illustrates the state diagram of the I/O Controller's controllerstate machine of the present disclosure.

FIG. 10A illustrates the serial input and parallel output circuitry ofthe Serial I/O Circuitry of FIG. 7.

FIG. 10B illustrates the timing of the serial input and parallel outputcircuitry of FIG. 10A.

FIG. 11A illustrates the parallel input and serial output circuitry ofthe Serial I/O Circuitry of FIG. 7.

FIG. 11B illustrates the timing of the parallel input and serial outputcircuitry of FIG. 11A.

FIG. 12A illustrates a controller communicating to an IC according tothe present disclosure.

FIG. 12B illustrates an IC communicating to a controller according tothe present disclosure.

FIG. 12C illustrates a controller communicating to two ICs according tothe present disclosure.

FIG. 12D illustrates one IC communicating to another IC according to thepresent disclosure.

FIG. 13 illustrates one IC communicating to two ICs according to thepresent disclosure.

FIG. 14A illustrates a controller communicating to an embedded corecircuit in an IC according to the present disclosure.

FIG. 14B illustrates an embedded core circuit in an IC communicating toa controller according to the present disclosure.

FIG. 14C illustrates a controller communicating to two embedded corecircuits in an IC according to the present disclosure.

FIG. 14D illustrates one embedded core circuit in an IC communicating toanother embedded core circuit in the IC according to the presentdisclosure.

FIG. 15 illustrates one embedded core circuit in an IC communicating totwo other embedded core circuits in the IC according to the presentdisclosure.

FIG. 16 illustrates serial input and output data frame synchronizationoccurring between a transmitting IC or core circuit and a receiving ICor core circuit according to the present disclosure.

FIG. 17 illustrates additional TAP controller states in which the serialinput and output operations of the present disclosure may be executed.

FIG. 18 illustrates the execution of the serial input and outputoperations of the present disclosure in the additional TAP controllerstates of FIG. 17.

DETAILED DESCRIPTION

FIG. 4 illustrates a scan path system 402 of ICs/cores that include TAPdomains plus additional I/O circuitry. The combination of the TAP domainand I/O circuitry is referred to as TAPIO 416. FIG. 4 is similar to FIG.3 in regard to the way the TDI, TDO, TCK, TMS, and TRST signals arecoupled between the TAPIOs 416 and controller 420. Controller 420 isdifferent from controller 320 in that it has been improved according tothe present disclosure to include the capability of communicating datato and from the TAPIOs 416 via the TMS and TCK connections. Controller420 maintains the conventional capability of controller 320 tocommunicate to the TAP domains of the TAPIOs 416 using the standard IEEE1149.1 serial protocol.

As seen in FIG. 4, the TCK connection between controller 420 and TAPIOs416 is shown as a bidirectional signal path, as opposed to theunidirectional signal path of the TCK connection in FIG. 3. When a TAPIO416 is selected for sending data to the controller 420 according to thepresent disclosure, the TCK connection becomes a data output from theTAPIO and a data input to the controller, and the TMS connection becomesa clock output from the controller and a clock input to the TAPIO.

When a TAPIO 416 is selected for receiving data from the controller 420according to the present disclosure, the TCK connection becomes a dataoutput from the controller and a data input to the TAPIO, and the TMSconnection becomes a clock output from the controller and a clock inputto the TAPIO. According to the present disclosure, the TMS and TCKconnections can be set up to operate as a serial bus with TMS serving asthe clock signal for the serial bus and TCK serving as the data input oroutput signal of the serial bus. As can be seen in FIG. 4, data may betransferred directly between a selected TAPIO 416 and controller 420.Therefore the data latency and shift frequency problems mentioned inregard with FIG. 3 do not exist in FIG. 4.

Additionally, according to the present disclosure, one TAPIO of anIC/core in the scan path 402 may communicate to another TAPIO of anIC/core in the scan path 402 via the TCK and TMS serial bus connectionsbetween them. To achieve this mode of operation, the controller 420selects one TAPIO to transmit and another TAPIO to receive. Thecontroller then disables its TCK output driver so that the transmittingTAPIO can output on its TCK terminal to send data to the TCK terminal ofthe receiving TAPIO. The controller outputs clocks on TMS to time thedata transfer between the transmitting and receiving TAPIOs. Again, thedata is directly transferred between the TAPIOs, via the TCK connection,without the aforementioned problems.

FIG. 5 illustrates the TAPIO circuit 416 in more detail. As seen theTAPIO 416 consists of a TAP domain 502, a Serial I/O communicationcircuit 514, AND gates 506-508, and a Sync Circuit 528. TAP domain 502is similar to TAP domain 102 with the exception that it includes ANDgate 504 for detecting when the TAP controller 104 is in the RunTest/Idle (RTI) state 202 of FIG. 2.

The TAP controller 104 is a four bit state machine defining the 16unique states shown in FIG. 2. Each of the 16 TAP states is defined by aunique one of the four bit state machine codes. While not shown, thefour inputs of the AND gate 504 are inverted or not inverted to allowthe AND gate to detect, with a logic high output, when the TAPcontroller 104 is in the Run Test/Idle state. For example, if the RunTest/Idle state has a four bit code of 0101, then the “0” inputs to ANDgate 504 will be inverted such that the AND gate will receive all “1's”at its inputs so that it outputs a logic one when the TAP controller isin the Run Test/Idle state. This will be the case throughout theremainder of this specification for all AND gates that are described foruse in detecting TAP controller states. Also while AND gates are shownbeing used to detect TAP controller states, other gating circuits may beused as well.

Further, TAP domain 502 differs from TAP domain 102 in that it includesan Enable Serial Output signal 510, an Enable Serial Input signal 512,and a I/O Sync signal 526. The Enable Serial Output signal is set by aJTAG scan operation whenever the Serial I/O communication circuit 514 isto perform a data output operation on TCK. The Enable Serial Inputsignal is set by a JTAG scan operation whenever the Serial I/Ocommunication circuit 514 is to perform a data input operation on TCK.The I/O Sync signal is set low when an IC or core within an IC performsa data input operation from the controller 420.

While I/O Sync is low, the output of AND gate 508 is coupled directly,via multiplexer 530 of Sync Circuit 528, to the Input Enable input ofthe Serial I/O Circuit 516. The I/O Sync signal is set high when an ICperforms a data input operation from another IC or when a core within anIC performs a data input operation from another core within the IC.

While I/O Sync is high, the output of AND gate 508 is coupled, via D-FF532 and multiplexer 530 of Sync Circuit 528, to the Input Enable inputof Serial I/O Circuit 516. The purpose and operation of the I/O Syncsignal 526 and Sync Circuit 528 will be described in more detail laterin regard to FIG. 16. As seen, the Enable Serial Input, Enable SerialOutput, and I/O Sync signals can come, by design choice, from either theIR 106 via bus 114 or from a DR 108 via bus 112.

When Enable Serial Output is set high and when the TAP controller 104 isin the Run Test/Idle (RTI) state 202, the output of AND gate 506 will gohigh to enable the Serial I/O communications circuit 514 to perform aserial TCK output operation. When Enable Serial Input is set high andwhen the TAP controller 104 is in the Run Test/Idle (RTI) state, theoutput of AND gate 508 will go high to enable the Serial I/Ocommunications circuit 514 to perform a serial TCK input operation.

If the I/O Sync signal is low, the high output of AND gate 508 willimmediately set the Input Enable input of Serial I/O Circuit 516 highvia multiplexer 530. If the I/O Sync signal is high, the high output ofAND gate 508 will set the Input Enable input of Serial I/O Circuit 516high following the first rising edge of a clock input on the TMS signal316. As seen in Sync Circuit 528, when I/O Sync is high, the input fromAND gate 508 must be clocked into D-FF 532 on the rising edge of the TMSclock before being output from multiplexer 530 to the Input Enable inputof Serial I/O Circuit 516. During serial TCK input or output operations,the controller 420 outputs a clock on TMS to time the serial operations.Also during either the serial TCK input or output operations, the TAPcontroller 104 remains in the Run Test/Idle state 202.

Serial I/O communication circuit 514 consists of a Serial I/O Circuit516, a Data Source circuit 522, and Data Destination circuit 524. TheSerial I/O Circuit 516 receives the Input Enable signal from AND gate508 (via Sync Circuit 528), the Output Enable signal from AND gate 506,a TCK 314 data input signal via connection 534 during serial inputoperations, parallel data input signals from Data Source circuit 522,and a TMS 316 clock input signal via connection 538. The Serial I/OCircuit 516 outputs a TCK 314 data output signal via connection 536during serial output operations, parallel data output signals to DataDestination circuit 524, and control signals to the Data Source 522 andData Destination 524 circuits.

When enabled for inputting data from TCK (Input Enable signal set high),the Serial I/O Circuit 516 is clocked by TMS 316 to receive serial TCK314 data via connection 534 and transfer it in parallel to the DataDestination circuitry 524. Data Destination circuitry 524 may be anycircuitry within an IC including but not limited to; (1) an address bus,(2) a data bus, (3) a Ram memory, (4) a Cache memory, (5) a registerfile, (6) a FIFO, (7) a register, (8) a processor, (9) a peripheralcircuit, or (10) a bus coupled to circuitry external to the IC.

When enabled for outputting data on TCK (Output Enable signal set high),the Serial I/O Circuit 516 is clocked by TMS 316 to receive paralleldata from the Data Source circuitry 522 and output the data serially onTCK via connection 536. Data Source circuitry 522 may be any circuitrywithin an IC including but not limited to; (1) an address bus, (2) adata bus, (3) a Ram memory, (4) a Rom memory, (5) a Cache memory, (6) aregister file, (7) a FIFO, (8) a register, (9) a processor, (10) aperipheral circuit, or (11) a bus coupled to circuitry external to theIC. The Data Destination 524 and Source 522 circuits may be functionalcircuits, test circuits, debug circuits, trace circuits, emulationcircuits, in-system programming circuits, or mixtures of these and/orother circuit types.

FIG. 6A illustrates a portion of the TAP controller state diagram ofFIG. 2 whereby the TAP controller 104 is seen to transition to andremain in the Run Test/Idle state 202. FIG. 6B illustrates a TCK and TMStiming diagram relating to the state transitions in FIG. 6A. The TAPcontroller samples the logic value of TMS on the rising edge 602 of TCKto transition between its states. As seen in FIGS. 6A and 6B, the TAPcontroller will transition from either the Update-DR or Update-IR stateto the Run Test/Idle state on the rising edge of TCK when TMS is at alogic zero. The TAP controller will remain in the Run Test/Idle stateduring each rising edge of TCK if the rising edge occurs while TMS is ata logic zero. The TAP controller will transition from the Run Test/Idlestate to the Select-DR state if TMS is a logic one during the risingedge of TCK.

In FIG. 6B it is seen that while the TAP controller is in the RunTest/Idle state, the TCK and TMS serial I/O operation of the presentdisclosure may be executed between times 604 and 606. During theexecution, TCK serves as either a serial data input to the TAPIO or aserial data output from the TAPIO, while TMS serves as a clock input tothe TAPIO for timing the serial data. To prevent the serial data inputor output operation of the present disclosure from causing a change ofstate in the TAP controller (i.e. causing the TAP controller totransition out of the Run Test/Idle state which would terminate theserial I/O operation) the timing of the TCK clock and TMS data must beorchestrated such that each rising edge of TCK data occurs only when theTMS clock is at a logic zero state.

FIG. 6C illustrates a portion of a serial data input or output operationoccurring between times 604 and 606 of FIG. 6B. In this portion, aserial data stream of “101” is shown being transferred on TCK while aclock is applied on TMS. As mentioned above, the timing of the TCK dataand TCK clock signals are orchestrated, as seen at times 608 of FIG. 6C,such that during each rising edge of a TCK data signal the TMS clocksignal is at a logic low state. Such timing orchestration of the TCKdata and TMS clock signals insures that the TAP controller 104 willremain in the Run Test/Idle state 202 during each rising edge 602 of aTCK data signal, since the value on the TMS clock signal will be a logiclow.

Use of this timing scheme on TCK and TMS by the present disclosureprevents the TAP controller from being effected by the serial I/Ooperation taking place on the TCK and TMS serial bus. When the TAPIO isreceiving serial data from the controller 420, the controller providesthe TCK and TMS signal timing of FIG. 6C. When the TAPIO is outputtingserial data to the controller 420 or to another TAPIO, the Serial I/Ocircuit 516 of the outputting TAPIO provides the TCK and TMS signaltiming of FIG. 6C.

FIG. 7 illustrates an example of a Serial I/O Circuit 516 in moredetail. The Serial I/O Circuit of this example consists of a shiftregister 702, an I/O controller 704, a bit counter 706, a frame counter740, an output D-FF 708, a 3-state buffer 710, and a delay circuit 712.The I/O controller 704 inputs the TMS 316 signal via connection 538, theInput Enable (IE) signal from AND gate 508 (via Sync Circuit 528), theOutput Enable (OE) signal from AND gate 506, a bit count complete (BCC)signal from bit counter 706, and a frame count complete (FCC) from framecounter 740.

The I/O controller outputs an Update signal, a Shift signal, a Clocksignal, a Load signal, an Out signal, and bit and frame counter controlsignals. The shift register has a serial input coupled to TCK 314 viaconnection 534, a serial output coupled to the input of D-FF 708,control inputs coupled to the Shift, Clock, and Load output signals fromI/O controller 704, a parallel output bus 716 coupled to DataDestination 524, and a parallel input bus 718 coupled to Data Source522.

The bit counter 706 receives control inputs from I/O controller 704 andoutputs a bit count complete (BCC) signal to I/O controller 704. Theframe counter 740 receives control input from I/O controller 704, aninput from TDI 746 of TAP domain 502, and control inputs 744 from theTAP controller and instruction register of TAP domain 502. The framecounter 740 outputs a TDO output 742 which is input to the multiplexer110 of the TAP domain 502 and outputs a frame count complete (FCC)signal to I/O controller 704. The frame counter is one of the dataregisters 108 that can be selected between TDI and TDO, via multiplexer110, for shifting in data (a frame count) during JTAG DR scanoperations. During serial data input and output operations, the framecounter 740 is controlled to count by the I/O controller 704.

During serial input operations, the frame count value shifted into theframe counter determines the number of serial data input frames thatwill be shifted in from TCK 314 via connection 534. During serial outputoperations, the frame count value shifted into the frame counterdetermines the number of serial data output frames that will be shiftedout onto TCK 314 via connection 536. The number of serial bits in aninput or output frame is determined by the count value in the bitcounter 706.

One example circuit 746 for implementing the bit counter 706 is shown toconsist of a fixed length down counter 747 which responds to controlinput from I/O controller 704, during serial input and output operationsof the disclosure, to load a fixed bit count value and perform countdown operations. When the bit count value reaches zero, the counter 747outputs the bit count complete (BCC) signal to I/O controller 704. Thisload and count operation repeats in response to further control inputfrom I/O controller 704.

One example circuit 748 for implementing the frame counter 740 is shownto consist of an N-bit JTAG accessible shift register 750 and a N-bitcount down counter 749. A JTAG DR scan operation shifts a desired framecount value into the shift register 750 then updates the frame countvalue from the shift register to the counter 749. During serial inputand output operations of the disclosure, the I/O controller 704 outputscontrol to cause the counter 749 to count until the frame count reacheszero, which causes the frame counter to output the frame count complete(FCC) signal to the I/O controller 704.

It should be understood that while the bit counter 706 is shown inexample 746 as being designed to operate from a fixed bit count value,it could alternately be designed, as is the frame counter 740, to allowa JTAG DR scan operation to load a desired bit count value into thecounter via a shift register.

The input to 3-state buffer 710 is coupled to the output of D-FF 708,the control input to the 3-state buffer is coupled to the Out signalfrom I/O controller 704, and the output of 3-state buffer is coupled toTCK 314 via connection 536. The input to the delay circuit 712 iscoupled to the Clock output of I/O controller 704 and the delayed clock(DCK) output of the delay circuit is coupled to the clock input of D-FF708. As will be discussed later in regard to FIGS. 11A and 11B, thecombination of the delay circuit 712 and D-FF 708 provide the circuitryrequired to achieve the desired timing orchestration between TCK dataand TMS clock signals during times when the TAPIO is outputting serialdata on TCK.

Shift register 702 includes a plurality of serially connected bitpositions 716 located between the shift registers serial input andserial output. In this example, each bit position is comprised of acircuit 714 that contains a multiplexer and a D-FF. As seen, themultiplexer of circuit 714 has inputs for receiving an input from DataSource 522 via bus 718, the Serial Input of circuit 714, and the outputof the D-FF of circuit 714. The multiplexer receives Load and Shiftcontrol inputs from I/O controller 704 and has an output coupled to theD-FF data input. The D-FF has a clock input coupled to the Clock outputof I/O controller 704 and a data output coupled to the Serial Output ofcircuit 714 and to the Data Destination 524 via bus 716.

The Serial Output of a leading circuit 714 is connected to the SerialInput of a following circuit 714 to form the serially connected bitpositions 716 between the serial input and output of shift register 702.As seen and during Clock inputs from I/O controller 704; (1) ifLoad:Shift=0:0 circuit 714 reloads the present state of the D-FF, (2) ifLoad:Shift=0:1 circuit 714 shifts data through the D-FF from the SerialInput to the Serial Output, and (3) if Load:Shift=1:0 circuit 714 loadsdata into the D-FF from Data Source 522.

When the Input Enable (IE) and Output Enable (OE) are both low, theSerial I/O circuit 516 is idle and no serial input or output operationsoccur. When Input Enable is high and Output Enable is low, the SerialI/O circuit 516 is enabled to input serial data from TCK 314 viaconnection 534 in response to clock inputs on TMS 316. Prior toperforming a serial input operation, the controller 420 will have loadeda frame count in frame counter 740 via a JTAG scan operation. Duringserial input operations, the I/O controller 704 is clocked by TMS andoperates to; (1) output control to load the bit counter 706 with a countindicative of the number of serial bits to receive from the TCK input,(2) output control to the shift register 702 (active Clock andLoad:Shift=0:1) to cause shift register to shift in TCK data until theshift register is filled, and (3) to output an Update signal to DataDestination 524 after the shift register fills to indicate that paralleldata is available on bus 716.

The I/O controller outputs control to the bit counter to count each timea data bit is shifted into the shift register from TCK. The count in thebit counter determines when the shift register is filled by outputtingthe bit count complete (BCC) signal to the I/O controller when the bitcount expires. When the I/O controller outputs the Update signal in step(3) it also outputs control to the bit counter to load it with the nextbit count value. The Update signal also causes the frame counter 740 tocount each time a frame of serial data has been shifted into shiftregister 702 from TCK 314.

The count in the frame counter determines when the selected number offrames has been shifted in by outputting the frame count complete (FCC)signal to the I/O controller when the frame count expires. In thisexample, the I/O controller pauses the shifting in of TCK data when itoutputs the Update signal by setting Load:Shift32 0:0. This sequence ofserially inputting data into the shift register from TCK 314 until itfills followed by updating the data in parallel to the Data Destinationis repeated until the serial input operation has been completed by theFCC signal from the frame counter going high. The FCC frame counteroutput goes high when the frame count value expires, which indicatesthat the selected number of serial input frames have been shifted infrom TCK 314.

When Input Enable is low and Output Enable is high, the Serial I/Ocircuit 516 is enabled to output serial data onto TCK 314 via connection536 in response to clock inputs on TMS 316. Prior to performing a serialoutput operation, the controller 420 will have loaded a frame count inframe counter 740 and will have disabled its TCK output from driving theTCK signal 314. During serial output operations, the I/O controller 704is clocked by TMS and operates to; (1) enable the 3-state buffer 710,via the Out control signal, to drive the TCK 314 signal, (2) outputcontrol to load the bit counter 706 with a count indicative of thenumber of serial bits to output on TCK, (3) output control to the shiftregister 702 (active Clock and Load:Shift=1:0) to cause shift registerto load parallel data from Data Source 522, and (4) output control tothe shift register (active Clock and Load:Shift=0:1) to cause the shiftregister to shift out data onto TCK 314 until the shift register isempty.

The Load control signal from the I/O controller in step (3) is alsooutput to the Data Source 522 to indicate to the Data Source that thepresent parallel data on bus 718 is being loaded into the shiftregister. The Load signal thus enables the Data Source to know when tofetch and output the next parallel data onto bus 718 for subsequentloading into the shift register. The Load signal also causes the framecounter 740 to count each time a frame of data has been loaded intoshift register 702 from Data Source 522. The count in the bit counterdetermines when the shift register is empty by outputting the bit countcomplete (BCC) signal to the I/O controller when the count expires. TheI/O controller outputs control to the bit counter to count each time adata bit is shifted out of the shift register onto TCK. When the shiftregister empties, the I/O controller outputs control to cause the bitcounter to reload, cause the shift register to load the next paralleldata pattern from Data Source 522, and cause the frame counter to count.

This sequence of parallel loading data into shift register 702 from DataSource 522 followed by serially outputting data from the shift registeronto TCK 314 until it empties is repeated until the serial outputoperation has been completed by the FCC output from the frame countergoing high. The FCC frame counter output goes high when the frame countvalue expires, which indicates that the selected number of serial outputframes have been loaded and shifted out onto TCK 314. The 3-state buffer710 remains enabled to drive TCK 314 until the frame counter outputs theFCC signal, which causes the I/O controller 704 to disable the outputdrive of the 3-state buffer via the Out signal. When the 3-state outputbuffer is disabled, the controller 420 can enable its TCK output toresume its conventional mode of driving the TCK signal 314.

FIG. 8 illustrates an example of the I/O controller circuit 704. The I/Ocontroller circuit consists of a controller state machine 802, OR gates804 and 832, AND gate 806, inverter 830, and D-FFs 808-815. Controllerstate machine 802 has a clock input coupled to the I/O controller's TMSclock signal via connection 538, data inputs coupled to the I/Ocontroller's Input Enable (IE), Output Enable (OE), bit count complete(BCC), and frame count complete (FCC) signals, and a reset input coupledto the Reset output 828 from OR gate 804. Controller state machine 802operates on the rising edge of the TMS clock input. Controller statemachine 802 outputs an active signal 816, a shift signal 818, a loadsignal 818, an update signal 822, an out signal 823, and a Load Countsignal 824.

The D-FF 808 inputs active signal 816 and outputs Active signal 826.D-FF 810 inputs shift signal 818 and outputs the I/O controller's Shiftsignal. D-FF 812 inputs load signal 820 and outputs the I/O controller'sLoad signal. D-FF 814 inputs update signal 822 and outputs the I/Ocontroller's Update signal. D-FF 815 inputs out signal 823 and outputsthe I/O controller Out signal.

The clock inputs to D-FFs 808-815 are connected to the TMS clock inputvia inverter 830 to allow the D-FFs to be clocked on the falling edge ofthe TMS clock input. The reset inputs to D-FF 808-815 are connected tothe Reset signal 828 from OR gate 804. OR gate 804 inputs the I/Ocontroller's IE and OE input signals and outputs the Reset signal 828.OR gate 832 inputs the I/O controller's Load and Update output signalsand outputs a frame counter clock signal 834. AND gate 806 inputs theTMS clock signal and the Active signal 826, and outputs the I/Ocontroller's Clock signal.

I/O controller 704 outputs the Reset signal 828, the Load Count signal824, and the I/O controller's Clock signal to bit counter 706. The I/Ocontroller outputs the frame counter clock signal 834 to the framecounter 740. These signals to the bit counter and frame counter form thecontrol input to the counters as shown in FIG. 7.

FIG. 9 illustrates the state diagram operation of the example controllerstate machine 802 of FIG. 8. The following description will referenceboth FIGS. 8 and 9. In the state diagram IE* indicates a low on IE, OE*indicates a low on OE, BCC* indicates a low on BCC, and FCC* indicates alow on FCC.

When the IE and OE signal are both low, the controller state machine 802will be in the Idle state 902 by the Reset output 828 from OR gate 804being low. The IE and OE signals will be set low at power up or reset ofthe IC/core they reside in. As previously described, the IE and OEsignals are set high by a JTAG IR or DR scan operation. In the Idlestate, the controller state machine's active 816, shift 818, load 820,update 822, out 823, and Load Count signals will be low. Also in theIdle state, the outputs (Active, Shift, Load, Update, and Out) of D-FFs808-815 will be low by Reset signal 828 being low. Further during theIdle state, the I/O controller's Clock output will be low since Activesignal 826 is low.

Due to Reset 828 being low, which forces the Idle state 902, thecontroller state machine is not responsive to signaling activity on theTMS signal. Thus while in the Idle state, the I/O controller 704 ignoresTMS signaling activity from controller 420 that occurs duringconventional JTAG TAP controller operations, such as IR and DR scanoperations.

When IE or OE go high, the controller state machine 802 will transitionfrom the Idle state 902 to the Active region 903 of the state diagram onthe rising edge of a TMS clock input to perform either a serial inputoperation (IE high) or a serial output operation (OE high). As seen inthis example, the serial input operation consists of Shift 904 andUpdate 906 states, and the serial output operation consists of Load 908and Shift 910 states. At the end of a serial input or output operation,the controller state machine 802 will exit the Active region of thestate diagram to enter the Stop state 912. When IE and OE are set low,the controller state machine 802 transitions from the Stop state 912 tothe Idle state 902.

When a serial input operation is to be performed, a JTAG scan operationwill have loaded the frame counter 740 (FCC is low) and set IE high andOE low. IE going high sets Reset 828 high, which removes the resetcondition on controller state machine 802, D-FFs 808-815, and bitcounter 706. The reset condition to bit counter 706 initializes the bitcounter with the appropriate count value, such that when the resetcondition is removed the bit counter is preloaded and prepared to count(BCC is low).

With Reset signal 828 high, controller state machine 802 is responsiveto TMS clock inputs to sample the state of the IE, OE, BCC, and FCCinputs. As seen in the state diagram, the controller responds to the IE& OE* input condition to transition from the Idle state 902 to the Shiftstate 904 on the rising edge of an applied TMS clock. The active 816 andshift 818 signals are set high upon entry into the Shift state. Theactive 816 output remains high while the controller state machine 802 isin the active region 903 of the state diagram. On the falling edge ofthe TMS clock, D-FFs 808 and 810 output highs on the Active and Shiftsignals respectively. The high on the Active signal enables AND gate 806to pass subsequent TMS clocks to the Clock output of the I/O controller704, which is connected to the shift register 702 and bit counter 706.

With the Shift signal high and Clock signal enabled, the shift register702 will shift in data from TCK via connection 534 during eachsubsequent TMS clock input and the bit counter will count the number ofshifts. The controller state machine 802 will remain in the Shift stateduring subsequent TMS clocks until the bit counter outputs a high on theBCC, indicating that a complete frame of data bits have been shiftedinto the shift register from TCK.

In response to BCC going high, the controller state machine transitionsto the Update state 906 on the rising edge of the TMS clock and setsshift 818 signal low, the update 822 signal high, and the Load Count 824signal high. On the falling edge of the TMS clock, the Shift output fromD-FF 810 goes low to pause the shift register from shifting and theUpdate output of D-FF 814 goes high to indicate to the Data Destinationthat parallel data from the shift register is available for input. TheUpdate output also causes the frame counter to perform a count operationvia the clock output 834 from OR gate 832.

If the FCC signal remains low after the frame counter has been clocked,indicating that at least one more serial input frame is to be performed,the bit counter reloads the bit count value on the next rising edge ofthe TMS clock (BCC goes low), since Load Count is high. The controllerstate machine 802 transitions back into the Shift state 904 setting LoadCount 824 and update 822 back low and shift 818 back high. On thefalling edge of the TMS clock, the Shift output of D-FF 810 goes high,and the Update output of D-FF 814 goes low. The controller state machine802 will remain in the Shift state 904 with the Shift signal high andClock signal enabled to shift in the next frame of data from TCK untilthe BCC input goes high again.

When BCC goes high, the controller state machine 802 will againtransition from the Shift state 904 to the Update state 906 where theShift output will again go low, and the Update and Load Count outputswill again go high. When Update goes high, the frame counter 740receives another clock input from OR gate 834 to perform another countoperation.

If the FCC output of the frame counter goes high in response to theUpdate clock output from OR gate 832, the frame count has expired andthe appropriate number of serial input frames has been received. WithFCC high, the controller state machine will transition on the nextrising edge of the TMS clock from the Update state 906 to the Stop state912 to exit the active region 903 of the state diagram and end theserial input operation. Upon entry into the Stop state 908, the active816, shift 818, load 820, update 822, out 823, and Load Count outputs ofcontroller state machine 802 go low. On the falling edge of the TMSclock in the Stop state 908, the Clock, Shift, Load, Update and Outsignals of the I/O controller go to and remain low. A JTAG IR or DR scanoperation can be executed to set IE and OE low to force the controllerstate machine from the Stop state 912 to the Idle state 902.

The above described process of shifting data frames from TCK into theshift register and updating the data frames in parallel to the DataDestination 524 repeats until the desired number of data frames havebeen serially input and updated to the Data Destination, as indicated byFCC going high. The above process is executed while the TAP controller104 is in a steady state as described previously in regard FIGS. 6A and6B.

When a serial output operation is to be performed, JTAG scan operationswill have loaded the frame counter 740 (FCC is low) and set IE low andOE high. OE going high sets Reset signal 828 high, which removes thereset condition on controller state machine 802, D-FFs 808-815, and bitcounter 706 (BCC is low). With Reset signal 828 high, controller statemachine is responsive to TMS clock inputs to sample the state of the IE,OE, BCC, and FCC inputs.

In the state diagram, the controller 802 responds to the IE* & OE inputcondition to transition from the Idle state 902 to the Load state 908 onthe rising edge of an applied TMS clock. The active 816, load 820, out823, and Load Count 824 signals are set high upon entry into the Loadstate. The active 816 and out 823 signal outputs will remain high whilethe controller state machine 802 is in the active region 903 of thestate diagram. On the falling edge of the TMS clock, D-FFs 808, 812, and815 output highs on the Active, Load, and Out signals respectively.

The high on the Out signal enables the 3-state buffer 710 to drive theTCK signal 314 via connection 536. 3-State buffer 710 is unopposed indriving the TCK signal 314 since controller 420 will have disabled itsdrive of the TCK signal 314 prior to the start of the serial outputoperation. The high on the Active signal enables AND gate 806 to passsubsequent TMS clocks to the Clock output of the I/O controller 704,which is connected to the shift register 702 and bit counter 706. Thehigh transition on the Load signal causes the frame counter 740 toperform a count operation via the clock output 834 of OR gate 832.

With the Load signal high and Clock signal enabled, the next rising edgeof the TMS clock will load a parallel data frame from Data Source 522into shift register 702 and will load the bit count value into the bitcounter (BCC is low) since the Load Count signal is high. The Loadsignal output to Data Source 22 indicates to the Data Source that thepresent parallel data frame has been loaded so that the Data Source canfetch the next parallel data frame to be loaded.

In response to the rising edge of the TMS clock that loads data from theData Source, the controller transitions from the Load state 908 to theShift state 910. Upon entry into the Shift state, the load signal 820and Load Count signal 824 go low and the shift signal 818 goes high. Onthe falling edge of the TMS clock, the Load output of D-FF 812 goes lowand the Shift output of D-FFs 810 goes high. With the Shift signal highand Clock signal enabled, the shift register 702 will shift out dataonto TCK via connection 536 during each subsequent TMS clock input andthe bit counter will count the number of shifts. The controller statemachine 802 will remain in the Shift state during subsequent TMS clocksuntil the bit counter outputs a high on the BCC signal, indicating thata complete frame of data bits have been shifted out of the shiftregister onto TCK.

If the FCC signal is low, indicating that the frame count in the framecounter has not expired, the controller state machine responds to theBCC signal to transition back into the Load state 908 on the rising edgeof the TMS clock to set shift 818 signal low, the load 820 signal high,and the Load Count 824 signal high. On the falling edge of the TMSclock, the Shift output from D-FF 810 goes low and the Load output fromD-FF 812 goes high. The high transition on the Load output signal causesthe frame counter 740 to perform another count operation, via the clockoutput 834 of OR gate 832.

On the next rising edge of the TMS clock the shift register loads thenext parallel data frame output from Data Source 522, the bit counter isreloads with the bit count (BCC is low) since Load Count is high, andthe controller state machine 802 transitions back into the Shift state910. The load signal 820 and Load Count signal 824 go low and the shiftsignal 818 goes high upon re-entry into the Shift state. On the fallingedge of the TMS clock, the Load output of D-FF 812 goes low and theShift output of D-FFs 810 goes high. With the Shift signal high andClock signal enabled, the shift register 702 will shift out the dataframe onto TCK via connection 536 during each subsequent TMS clock inputand the bit counter will count the number of shifts.

The controller state machine 802 remains in the Shift state duringsubsequent TMS clocks until the bit counter again outputs the BCCsignal, indicating again that a complete frame of data bits have beenshifted out of the shift register onto TCK.

If FCC is high, indicating that the frame count in the frame counterexpired on the last Load signal clock input from OR gate 832, thecontroller state machine will respond to the high on the BCC signal totransition from the Shift state 910 to the Stop state 912 on the risingedge of the TMS clock to exit the active region 903 of the state diagramand end the serial output operation. Upon entry into the Stop state, theactive 816, shift 818, load 820, update 822, out 823, and Load Countoutputs of controller state machine 802 go low. On the falling edge ofthe TMS clock in the Stop state, the Clock, Shift, Load, Update and Outsignals of the I/O controller go to and remain low. A JTAG IR or DR scanoperation can be executed to set IE and OE low to force the controllerstate machine from the Stop state 912 to the Idle state 902.

As seen from the description above, the serial output operation willcontinue to load and shift out data frames onto TCK until the controllerstate machine recognizes the input condition where both BCC and FCC arehigh (i.e. BCC & FCC). This condition occurs when the frame count hasexpired and the last bit of the last frame has been shifted out onto TCK314. When this condition is recognized, the controller state machinewill transition from the Shift state 910 to the Stop state 912 anddisable further load and shift out operations. The above process isexecuted while the TAP controller is in a steady state as describedpreviously in regard FIGS. 6A and 6B.

It is important to note that the I/O controller's Out signal will go lowin the Stop state 912 to disable the output drive of the 3-state buffer710. This is an important feature in that it allows the controller 420to enable its TCK output to regain drive control of the TCK signal line.The frame counter's ability to count the number of frames and toindicate to the controller state machine 802, via the FCC signal, whenthe last frame is being sent allows the controller state machine totransition to the Stop state after the last bit of the last frame hasbeen sent to disable the drive of the 3-state buffer 710.

Without this indication from the frame counter and the response to theindication by the controller state machine, the 3-state buffer 710 couldnot be disabled, which would not allow the controller 420 to enable itsTCK output and regain drive control of the TCK signal line. When thecontroller 420 regains drive control of the TCK signal line, it canperform the above mentioned JTAG IR or DR scan operation to set IE andOE low to force the controller state machine from the Stop state 912 tothe Idle state 902.

FIG. 10A illustrates the serial input operation whereby the shiftregister 702 shifts in data from TCK and updates the data to DataDestination 524. FIG. 10B illustrates the timing of the serial inputoperation. As seen in FIG. 10B, the serial input operation will begin bythe controller state machine 802 transitioning from the Idle state 902to the Shift state 904 in the Active region 903 of the state diagram.The dotted line clock 1002 on the Clock signal of the timing diagramindicates the TMS clock input that causes the transition from the Idlestate to the Shift state.

In the Shift state, the I/O controller 704 will output a high on itsShift output and clocks (continuous line clocks) on its Clock output tocause the shift register 702 to input a data frame (alternating 1's and0's in this example) from TCK. When the shift register fills with data(BCC is high) the I/O controller 704 will transition to the Update state906 to set the Shift output low and the Update output high. DataDestination 524 responds to the high on the Update output to load theparallel data frame from shift register 702 via bus 716. From the Updatestate, the I/O controller may transition back to the Shift state 904(FCC is low) to input another frame of data or transition to the Stopstate 912 (FCC is high) to end the serial input operation. This shift inand update process repeats until the overall serial input operation hasbeen completed with the controller state machine in the Stop state.

It is important to notice in the timing diagram of FIG. 10B that the TMSdriven clock pulses on the Clock output of I/O controller 704 appearonly during times when the TCK data input is in a stable logic one orzero state and that the TMS driven Clock output of I/O controller 704 isalways low when a data transition occurs on the TCK data input,especially the rising edge TCK data transitions. As mentioned previouslyin regard to FIGS. 6B and 6C, the controller 420 orchestrates this TCKand TMS timing during serial input operations to a TAPIO 416 to preventthe TAP controllers 104 of TAPIOs 416 from seeing a logic high on TMSduring a rising edge on TCK. If this were to occur the TAP controllers104 would transition from the Run Test/Idle state and disrupt the serialinput operation.

FIG. 11A illustrates the serial output operation whereby the shiftregister 702 loads data from Data Source 522 and shifts out the data onTCK. FIG. 11B illustrates the timing of the serial output operation. Asseen in FIG. 11B, the serial output operation will begin by thecontroller state machine 802 transitioning from the Idle state 902 tothe Load state 908 of the Active region 903 of the state diagram. Thedotted line clock 1104 on the Clock signal of the timing diagramindicates the TMS clock input that causes the transition from the Idlestate to the Load state 908.

In the Load state 908, the I/O controller's Out output is set to enablethe 3-state buffer 710 to drive the TCK signal via connection 536. Inthe Load state 908, the I/O controller 704 will output a high on itsLoad output and a clock (continuous line clock) on its Clock output tocause the shift register 702 to load a data frame (alternating 1's and0's in this example) from Data Source 522 via bus 718. As previouslymentioned, Data Source 522 initiates the fetching of the next data frameto load in response seeing the Load output high.

Following the load, the I/O controller 704 transitions to the Shiftstate 910 to set its Load output low and its Shift output high to shiftout the data frame on TCK during Clock outputs (continuous line clocks).In the Shift state, the I/O controller's Out output remains set toenable the 3-state buffer 710 to drive the TCK signal via connection536. When the shift register has shifted out the first frame of data andif a second frame is to be loaded and sent (BCC & FCC* condition), theI/O controller 704 transitions from the Shift state to the Load state toset its Shift output low and its Load output high to load the nextparallel data frame from Data Source 522.

After all data frames have been loaded and shifted out (BCC & FCCcondition), the I/O controller 704 will transition from the Shift state910 to the Stop state 912 to terminate the serial output operation anddisable the 3-state output buffer 710 by setting the Out signal low. Asseen in the timing diagram, in the Stop state the Clock output is gatedlow by And gate 806 to prevent further TMS clocks 1106, if any, frombeing output on the Clock output.

It is important to notice in the timing diagram of FIG. 11B that the TMSclock pulses driving the Clock output of I/O controller 704 appear onlyduring times when the TCK data output is in a stable logic one or zerostate and that the TMS clock pulses are always low when a datatransition occurs on the TCK data output, especially the rising edge TCKdata output transitions.

As mentioned previously in regard to FIG. 7, the Delay Circuit 712 andD-FF 708 of the Serial I/O circuit 516 provide the circuitry toorchestrate the timing of the TCK data output from 3-state buffer 710such that data transitions, especially rising edge data transitions, onthe TCK output only occur when the TMS clock pulses are in a low logicstate, as seen in the TCK and TMS driven Clock signal timing of FIG.11B. This TCK and TMS driven Clock signal timing during serial outputoperations from TAPIO 416 prevents the TAP controllers 104 of TAPIOs 416from seeing a logic high on TMS when a rising edge occurs on TCK, whichwould cause the TAP controllers to transition from the Run Test/Idlestate and disrupt the serial output operation.

As shown in FIG. 7, the Delay circuit 712 can be simply a string ofinverters which input the TMS driven Clock signal from I/O Controller704 and output a delayed and inverted DCK signal 1102. The DCK signal1102 is input to the clock input of D-FF 708. On each rising edge of theDCK signal, D-FF 708 inputs the serial data output of shift register 702and outputs the data on TCK via 3-state buffer 710. By using Delaycircuit 712 in combination with D-FF 708 the TCK data transitions in thetiming diagram of FIG. 11B occur such that during TCK data transitionsthe TMS driven Clock signal output from I/O Controller 704 is in a lowlogic state. While Delay circuit 712 and D-FF 708 provide one example ofhow to delay the TCK output signal such that TCK data output transitionsoccur while the TMS driven Clock signal is in a low logic state, othercircuit examples could be devised to achieve the same goal.

FIGS. 12A through 12D illustrate a system example consisting of two ICs1202 and 1204, each with a TAPIO 416 that is coupled to controller 420via TMS and TCK signal paths. The TCK terminal of each IC is connectedto input buffer 116 of FIG. 5 and 3-state output buffer 710 of FIG. 7.The 3-state output buffer 710 is shown external to the TAPIO forclarity. The TMS terminal of each IC is coupled to input buffer 118 ofFIG. 5. The enable input of each 3-state output buffer 710 is controlledby the Out signal 1203 of the I/O controller of TAPIOs 416.

The TMS terminal of the controller 420 is connected to an output buffer1214 and the TCK terminal of the controller 420 is connected to an inputbuffer 1212 and an output buffer 1208. Control circuitry 1206 incontroller 420 is coupled to buffers 1208, 1212, and 1214 to allow thecontroller 420 to input or output on TCK and to output on TMS. As seen,the control circuitry has an enable output 1210 to output buffer 1208 toallow the TCK terminal of the controller 420 to operate as either aninput or an output. The control circuitry 1206 is designed to operatethe TCK and TMS terminals according to either the IEEE 1149.1 standard(JTAG) timing whereby TMS and TCK both operate as outputs, or the timingof the present disclosure whereby TMS operates as an output while TCKmay operate as either an output or an input.

In FIG. 12A, the TAPIO 416 of IC 1202 has been set by a JTAG scan fromcontroller 420 to perform a serial input operation (IE high and OE low)from controller 420 according to the present disclosure, and the TAPIO416 of IC 1204 has been set by the JTAG scan not to perform anyoperation (IE and OE both low). During the serial input operation, thecontroller puts the TAP controllers 104 of the TAPIOs 416 in the RunTest/Idle state and outputs TMS clocks and TCK data to the TAPIO of IC1202. The flow of data from the TCK terminal of controller 420 to theTAPIO 416 of IC 1202 is shown in dotted line and passing throughdarkened buffers. As seen the 3-state buffer 710 of ICs 1202 and 1204are disabled via Out signal 1203 during the serial input operation toallow the controller 420 to input data to the TAPIO of IC 1202 via theTCK path. This method of serial communication allows data from thecontroller 420 to be quickly transferred to an IC's TAPIOs.

In FIG. 12B, the TAPIO of IC 1202 has been set by a JTAG scan fromcontroller 420 to perform a serial output operation (IE low and OE high)to controller 420 according to the present disclosure, and the TAPIO ofIC 1204 has been set by the JTAG scan to not perform any operation (IEand OE both low). To start the serial output operation, the controllerputs the TAP controllers 104 of the TAPIOs 416 in the Run Test/Idlestate, disables its TCK output buffer 1208, and outputs TMS clocks tothe TAPIO of IC 1202.

The TAPIO of IC 1202 responds by enabling 3-state buffer 710 via Outsignal 1203 and outputting data from its TCK terminal to the TCKterminal of controller 420. The data flow is shown by the dotted lineand passing through darkened buffers. The 3-state buffer 710 of IC 1204is disabled during the serial output operation from IC 1202. At the endof the serial output operation, the TAPIO of IC 1202 disables the3-state output buffer 710 to allow the controller to regain drivecontrol of the TCK signal path. This method of serial communicationallows data from an IC's TAPIO to be quickly transferred to a controller420.

In FIG. 12C, the TAPIOs 416 of ICs 1202 and 1204 have both been set by aJTAG scan from controller 420 to perform a serial input operation (IEhigh and OE low) from controller 420 according to the presentdisclosure. During the serial input operation, the controller puts theTAP controllers 104 of the TAPIOs 416 in the Run Test/Idle state andoutputs TMS clocks and TCK data to the TAPIOs of ICs 1202 and 1204. Theflow of data from the TCK terminal of controller 420 to the TAPIOs ofICs 1202 and 1204 is shown in dotted line and passing through darkenedbuffers.

As seen, the 3-state buffer 710 of ICs 1202 and 1204 are disabled viaOut signals 1203 during the serial input operation to allow thecontroller to input data to the TAPIOs of both ICs via the TCK path.FIG. 12C illustrates that a controller 420 can perform a serial inputoperation to a plurality of IC resident TAPIOs simultaneously. EachTAPIO will receive the same serial data input frames from the controller420. This method of serial communication allows data from a controller420 to be quickly transferred to a plurality of IC TAPIOs at the sametime. For example, this method of serial communication could be usedquickly to upload common data frames to multiple TAPIOs to enableparallel test, trace, emulation, in-system-programming, or functionaloperations in multiple ICs.

Use of the parallel serial input method of FIG. 12C requires the inputframes to have the same number of bits, which implies the serial bitlength of the shift register 702 of the TAPIOS 416 will be the samelength. The frame counters 740 of each TAPIO 416 may be loaded with thesame or different frame count. If loaded with the same frame count, bothTAPIOs will input the same number of frames then stop. However it ispossible to load one TAPIO with a first frame count and the other TAPIOwith a second frame count that is larger than the first frame count.

In this case, both TAPIOs 416 would input frames until the first framecount expires, which would causes the TAPIO with the first frame countto stop inputting frames. The TAPIO with the second frame count wouldcontinue to input frames until its frame count expires then it wouldstop. Thus by loading different frame counts into different TAPIOs, itis possible to continue to input frames to TAPIOs with larger framecounts after TAPIOs with smaller frame counts have stopped their serialinput operations by going to the Stop state 912.

In FIG. 12D, the TAPIO 416 of IC 1202 has been set by a JTAG scan fromcontroller 420 to perform a serial output operation (IE low and OE high)and the TAPIO 416 of IC 1204 has been set by the JTAG scan operation toperform a serial input operation (IE high and OE low) according to thepresent disclosure. With this setting the TAPIO of IC 1202 becomes atransmitter for outputting data on TCK and the TAPIO of IC 1204 becomesa receiver for inputting data from TCK.

During the serial operations, the controller 420 puts the TAPcontrollers 104 of the TAPIOs 416 in the Run Test/Idle state, disablesits TCK output buffer 1208, and outputs TMS clocks to the TAPIOs 416 ofICs 1202 and 1204. The flow of data from the TCK terminal of IC 1202 tothe TCK terminal of IC 1204 is shown in dotted line and passing throughdarkened buffers. When the IC to IC data communication has beencompleted, the TAPIO of IC 1202 disables its 3-state buffer 710 to allowthe controller 420 to regain control of the TCK signal path. Similar ICto IC communication can occur from IC 1204 to IC 1202 by simplyreversing the transmitter and receiver roles of the TAPIOs. This methodof serial communication allows data from one IC's TAPIO to be quicklytransferred to another IC's TAPIO.

FIG. 13 illustrates a system with a controller 420 coupled to TAPIOs ofICs 1202, 1204, and 1302 via TCK and TMS. In FIG. 13, the TAPIO 416 ofIC 1202 has been set by a JTAG scan from controller 420 to perform aserial output operation (IE low and OE high) and the TAPIOs 416 of ICs1204 and 1302 have been set by the JTAG scan operation to perform aserial input operation (IE high and OE low) according to the presentdisclosure. With this setting the TAPIO of IC 1202 becomes a transmitterfor outputting data on TCK and the TAPIOs of ICs 1204 and 1302 becomereceivers for inputting data from TCK. During the serial operations, thecontroller puts the TAP controllers 104 of the TAPIOs in the RunTest/Idle state, disables its TCK output buffer 1208, and outputs TMSclocks to the TAPIOs of ICs 1202, 1204, and 1302. The flow of data fromthe TCK terminal of IC 1202 to the TCK terminal of ICs 1204 and 1302 isshown in dotted line and passing through darkened buffers.

When the single IC to multiple IC data communication has been completed,the TAPIO of IC 1202 disables its 3-state buffer 710 to allow thecontroller 420 to regain control of the TCK signal path. FIG. 13 simplyillustrates that a TAPIO 416 of one IC can communicate data to aplurality of TAPIOs 416 in other ICs. As with the plural datacommunication described in regard to FIG. 12C, the frame counters of thereceiving TAPIOs of ICs 1204 and 1302 can be set to the same ordifferent frame counts. The frame counter of the transmitting TAPIO ofIC 1202 will be set to a frame count equal to the largest frame countloaded into the receiving TAPIOs. This method of serial communicationallows data from one IC's TAPIO to be quickly transferred to a pluralityof other IC TAPIOs.

FIGS. 14A through 14D illustrate a system with a controller 420 coupledto TAPIOs 416 of embedded core subcircuits 1404 and 1406 within an IC1402 via TCK and TMS. When multiple TAPIOs in a single IC are coupled tothe controller 420, the output of the IC's TCK 314 input buffer 116 iscoupled to all the TAPIO TCK inputs via connection 534 and the TCKoutput of each TAPIOs 3-state buffer 710 is coupled to the TCK terminal314 of the IC via connections 536. In this arrangement the ICs TCKterminal 314 can input to all TAPIO TCK inputs via input buffer 116 andconnection 534 and each TAPIO TCK output can be enabled to drive theIC's TCK terminal 314 via the TAPIO's 3-state buffer 710 and connection536.

In FIG. 14A, the TAPIO 416 of core 1404 has been set by a JTAG scan fromcontroller 420 to perform a serial input operation (IE high and OE low)from controller 420 according to the present disclosure, and the TAPIO416 of core 1406 has been set by the JTAG scan not to perform anyoperation (IE and OE both low). During the serial input operation, thecontroller puts the TAP controllers 104 of the TAPIOs 416 in the RunTest/Idle state and outputs TMS clocks and TCK data to the TAPIO of core1404. The flow of data from the TCK terminal of controller 420 to theTAPIO 416 of core 1404 is shown in dotted line and passing throughdarkened buffers. As seen the 3-state buffer 710 of cores 1404 and 1406are disabled via Out signal 1203 during the serial input operation toallow the controller 420 to input data to the TAPIO of core 1404 via theTCK path. This method of serial communication allows data from thecontroller 420 to be quickly transferred to an embedded core's TAPIOs.

In FIG. 14B, the TAPIO of core 1404 has been set by a JTAG scan fromcontroller 420 to perform a serial output operation (IE low and OE high)to controller 420 according to the present disclosure, and the TAPIO ofcore 1406 has been set by the JTAG scan to not perform any operation (IEand OE both low). To start the serial output operation, the controllerputs the TAP controllers 104 of the TAPIOs 416 in the Run Test/Idlestate, disables its TCK output buffer 1208, and outputs TMS clocks tothe TAPIO of core 1404. The TAPIO of core 1404 responds by enabling3-state buffer 710 via Out signal 1203 and outputting data from its TCKterminal to the TCK terminal of controller 420.

The data flow is shown by the dotted line and passing through darkenedbuffers. The 3-state buffer 710 of core 1406 is disabled during theserial output operation from core 1404. At the end of the serial outputoperation, the TAPIO of core 1404 disables the 3-state output buffer 710to allow the controller to regain drive control of the TCK signal path.This method of serial communication allows data from an embedded core'sTAPIO to be quickly transferred to a controller 420.

In FIG. 14C, the TAPIOs of cores 1404 and 1406 have both been set by aJTAG scan from controller 420 to perform a serial input operation (IEhigh and OE low) from controller 420 according to the presentdisclosure. During the serial input operation, the controller puts theTAP controllers 104 of the TAPIOs 416 in the Run Test/Idle state andoutputs TMS clocks and TCK data to the TAPIOs of cores 1404 and 1406.

The flow of data from the TCK terminal of controller 420 to the TAPIOsof cores 1404 and 1406 is shown in dotted line and passing throughdarkened buffers. As seen the 3-state buffer 710 of cores 1404 and 1406are disabled via Out signals 1203 during the serial input operation toallow the controller to input data to the TAPIOs of both cores via theTCK path.

FIG. 14C illustrates that a controller 420 can perform a serial inputoperation to a plurality of embedded core TAPIOs simultaneously. EachTAPIO will receive the same serial data input frames from the controller420. This method of serial communication allows data from a controller420 to be quickly transferred to a plurality of core TAPIOs at the sametime. For example, this method of serial communication could be usedquickly to upload common data frames to multiple TAPIOs 416 to enableparallel test, debug, trace, emulation, in-system-programming, orfunctional operations in multiple cores. Use of the parallel serialinput method to the plural embedded cores of FIG. 14C is similar to thatdescribed for the plural ICs in FIG. 12C in regard to shift register 702bit length and frame counts.

In FIG. 14D, the TAPIO 416 of core 1404 has been set by a JTAG scan fromcontroller 420 to perform a serial output operation (IE low and OE high)and the TAPIO 416 of core 1406 has been set by the JTAG scan operationto perform a serial input operation (IE high and OE low) according tothe present disclosure. With this setting the TAPIO of core 1404 becomesa transmitter for outputting data on it TCK output terminal and theTAPIO of core 1406 becomes a receiver for inputting data from its TCKinput terminal.

During the serial operations, the controller puts the TAP controllers104 of the TAPIOs in the Run Test/Idle state, disables its TCK outputbuffer 1208, and outputs TMS clocks to the TAPIOs of cores 1404 and1406. The flow of data from the TCK output terminal of core 1404 to theTCK input terminal of core 1406 is shown in dotted line and passingthrough darkened buffers. When the core to core data communication hasbeen completed, the TAPIO of core 1404 disables its 3-state buffer 710to allow the controller 420 to regain control of the TCK signal path.Similar core to core communication can occur from core 1406 to core 1404by simply reversing the transmitter and receiver roles of the TAPIOs.This method of serial communication allows data from one embedded core'sTAPIO to be quickly transferred to another embedded core's TAPIO.

FIG. 15 illustrates a system with a controller 420 coupled to TAPIOs 416of embedded cores 1404, 1406, and 1504 in an IC 1502 via TCK and TMS. InFIG. 15, the TAPIO of core 1404 has been set by a JTAG scan fromcontroller 420 to perform a serial output operation (IE low and OE high)and the TAPIOs of cores 1406 and 1504 have been set by the JTAG scanoperation to perform a serial input operation (IE high and OE low)according to the present disclosure.

With this setting the TAPIO of core 1404 becomes a transmitter foroutputting data on its TCK output terminal and the TAPIOs of cores 1406and 1502 become receivers for inputting data from their TCK inputterminals. During the serial operations, the controller puts the TAPcontrollers 104 of the TAPIOs in the Run Test/Idle state, disables itsTCK output buffer 1208, and outputs TMS clocks to the TAPIOs of cores1404, 1406, and 1504. The flow of data from the TCK output terminal ofcore 1404 to the TCK input terminals of cores 1406 and 1504 is shown indotted line and passing through darkened buffers.

When the single core to multiple core data communication has beencompleted, the TAPIO of core 1404 disables its 3-state buffer 710 toallow the controller 420 to regain control of the TCK signal path. FIG.15 simply illustrates that a TAPIO of one embedded core can communicatedata to a plurality of TAPIOs in other embedded cores. As with theplural data communication described in regard to FIG. 12C, the framecounters of the receiving TAPIOs of cores 1406 and 1504 can be set tothe same or different frame counts. The frame counter of thetransmitting TAPIO of core 1404 will be set to a frame count equal tothe largest frame count loaded into the receiving TAPIOs. This method ofserial communication allows data from one embedded core's TAPIO to bequickly transferred to a plurality of other embedded core TAPIOs.

When a TAPIO is transmitting data frames to another TAPIO, as shown inFIGS. 12D, 13, 14D, and 15, the receiving TAPIO has to be synchronizedwith the transmitting TAPIO using the previously mentioned I/O Syncsignal 526 and Sync Circuit 528 of FIG. 5. Referring back to FIG. 5 itis seen that if the I/O Sync signal is set to a logic one, the SyncCircuit 528 delays the output of the Input Enable signal to the SerialI/O Circuit 516 when the TAP controller 104 enters the Run Test/Idlestate (RTI goes high) until after the first rising edge of the TMS clockoccurs. Thus, by setting the I/O Sync signal high, the serial inputoperation of a receiving TAPIO may be delayed from starting by one TMSclock input.

By delaying the start of the serial input operation of the receivingTAPIO by one TMS clock, the transmitting TAPIO is given time to performits shift register 702 load operation. Following the shift register loadoperation, both the transmitting and receiving TAPIOs start their shiftout and shift in operation, respectively, on the same TMS clock input.Once started, the TAPIOs operate in sync with one another to transmitand receive same length data frames.

FIG. 16 illustrates the transmitting circuitry of a TAPIO 1602 in an ICor core starting up a communication session with the receiving circuitryof another TAPIO 1604 in an IC or core. In this example the shiftregisters 702 of the transmitting 1602 and receiving 1604 TAPIOs are ofthe same bit length. The I/O Sync signal 526 of the receiving TAPIO 1604has been set high to delay the start of the shift in operation of TAPIO1604 by one TMS clock input, via the Sync Circuit 528.

As seen in the “Load/Shift Out” operation 1616 of the transmitting TAPIO1602 and “Shift In/Update” operation 1618 of the receiving TAPIO 1604,the start of the first “Shift In” portion 1612 of the “Shift In/Update”operation 1618 is Delayed at 1610 until after the “Load” portion 1606 ofthe first “Load/Shift Out” 1616 operation has been performed. Thus thereceiving TAPIO 1604 is forced by the I/O Sync signal 526 and SyncCircuit 528 to delay its “Shift In” operation until the transmittingTAPIO begins its “Shift Out” operation. As seen in the overlayed TAPIO1602 and 1604 operation example 1620, after the initial TAPIO 1604 Delayat time 1610 the operations of the transmitting and receiving TAPIOs aresynchronized, such that when TAPIO 1602 shifts out at 1608, TAPIO 1604shifts in at 1612, and when TAPIO 1602 Loads at 1606, TAPIO 1604 Updatesat 1614.

FIG. 17 is provided to illustrate that other TAP controller states, inaddition to the Run Test/Idle state, may be used to perform serial inputand output operations according to the disclosure. For example, theShift-IR state, the Shift-DR state, the Pause-IR state, and the Pause-DRstate may be used along with the Run Test/Idle state as steady states inwhich serial input or output operations may be performed.

To use these additional TAP controller steady states to enable theserial input and output operations of the disclosure is simply a matterof providing AND gates 1702 to detect when the TAP controller is in oneof the states, as AND gate 504 did for detecting the Run Test/Idlestate, and providing an OR gate 1704 for indicating when any of the ANDgate 1702 outputs are high. The Serial I/O State output of OR gate 1704would be substituted for the RTI output of AND gate 504 in FIG. 5 andinput to And gates 506 and 508.

With this substitution made, the TAP controller 104 could betransitioned into any one of these steady states, and held there byadhering to the TCK and TMS signal timing restrictions described inFIGS. 6B and 6C, to allow a serial input or output operation to bestarted, executed, and stopped, as was described in regard to the RunTest/Idle state of FIG. 6A.

While it is possible to use the Shift-DR and Shift-IR states as steadystates for the serial input or output operations of the presentdisclosure, one must be aware that data will be shifting through the TAPDomains of the ICs/cores in the JTAG scan path from TDI to TDO, sincethe data transitions occurring on the TCK signal during serial input oroutput operations will be seen as TCK clocks for shifting data orinstruction on the TDI and TDO scan path. This may or may not be adesired situation and is therefore left up to the user of the disclosureto determined whether or not the Shift-IR and Shift-DR states should beused as steady states for use by the present disclosure.

FIG. 18 illustrates each of the TAP controller 104 states of FIG. 17being used as steady states to enable the serial input or outputoperation of the present disclosure. By adhering to the TCK and TMStiming restrictions described in FIGS. 6B and 6C, the TAP controllerwill remain in each of the these states while TCK and TMS Serial I/Ooperations take place.

Although the present disclosure has been described in detail, it shouldbe understood that various changes, substitutions, and alterations maybe made without departing from the spirit and scope of the disclosure asdefined by the appended claims.

1. An electrical device comprising: A. a TDI lead, a TDO lead, a TMSlead, and a TCK lead; B. test access port circuitry having a TDI inputcoupled to the TDI lead, a TDO output coupled to the TDO lead, a TMSinput coupled to the TMS lead, and a TCK input coupled to the TCK lead,an enable serial output lead, an input/output sync lead, and a RunTest/Idle lead; C. gate circuitry having an input connected to theenable serial output lead, another input connected to the Run Test/Idleoutput lead, and an output; and D. sync circuitry having a first inputconnected to the gate circuitry output, a second input connected to theinput/output sync lead, a clock input coupled to the TMS lead, and anoutput enable output.
 2. The device of claim 1 in which the test accessport circuitry includes an instruction register and a data register,both connected to the TDI input, and the enable serial output lead iscoupled to one of the instruction register and the data register.
 3. Thedevice of claim 1 in which the test access port circuitry includes aninstruction register and a data register, both connected to the TDIinput, and the input/output sync lead is coupled to one of theinstruction register and the data register.
 4. The device of claim 1 inwhich the test access port circuitry includes controller circuitryhaving state output leads, and logic circuitry having inputs connectedto the state output leads and having an output connected to the RunTest/Idle lead.